The present invention relates to an image forming apparatus for use with a paper cassette containing copy paper and removably attached to the main body of the apparatus for feeding the paper to the apparatus. Typical of such apparatus is a copying machine.
A paper cassette serving also as a storage case is disclosed in Unexamined Japanese Utility Model Application SHO 61-56335. Further various copy papers are in use which differ in size, thickness, talc content, quality, etc. To obtain copy or like images of improved quality, it is desired to form the image under conditions in conformity with these characteristics of copy paper.
The paper cassette serving also as a storage case initially contains a predetermined number of copy sheets. However, since the cassette is closed, it is difficult for the user to readily recognize the number of remaining sheets during use. To detect the number of sheets remaining in the cassette, means is conventionally used for detecting the thickness of stack of the sheets therein, but such means has the problem that since the thickness of copy paper is not uniform, the detected thickness does not always indicate the accurate number of remaining sheets. The detecting means, which comprises a plurality of sensors or a pulse disk, has another problem in that it is complex in construction and costly.